Precision Medicine: SCN8A Encephalopathy Treated with Sodium Channel Blockers

Epilepsy genetics in the paediatric population of the Eastern Anatolia region of Turkey

This study investigates the genetic causes of epilepsy in 166 paediatric patients under the age of 16 from the East Anatolian region of Turkey, who were treated at Erzurum City Hospital between 2018 and 2023. Patients with early-onset seizures, a family history of epilepsy or intellectual disability was selected for genetic analysis using a next-generation sequencing (NGS) gene panel targeting 449 genes associated with epilepsy and epileptic encephalopathy. The analysis revealed that pathogenic or probable pathogenic mutations were present in 14.8% (32 patients), highlighting the significant role of genetic factors in the aetiology of epilepsy in this population. In addition, 30.6% (66 patients) carried variants of uncertain significance (VUS), which, although not classified as pathogenic, have potential clinical relevance. Many epilepsy-related genes follow an autosomal dominant inheritance pattern, meaning that VUSs may gain pathogenic significance as more data and global studies accumulate, emphasising the evolving nature of genetic research. In addition to genetic factors, other aetiological causes such as perinatal insults (15.3%) and infections (7.9%) were identified, highlighting the multifactorial origin of epilepsy. While pathogenic mutations currently serve as important diagnostic and therapeutic markers, the role of VUS should not be underestimated. Genetic testing has proven to be essential for understanding the complex causes of epilepsy, providing opportunities for personalised treatment and genetic counselling. This study highlights the importance of genetic testing in regions such as Eastern Anatolia, where both environmental and genetic factors may influence the prevalence of epilepsy. As genetic databases expand, it is likely that the understanding of VUS will evolve, improving the clinical management of epilepsy through more targeted therapies and improved outcomes.

Genome-Based Therapeutics: Era of Precision Medicine in Genetic Epilepsies and Epileptic Encephalopathies

Introduction

The recent evolution of genomics has led to the development of targeted therapeutics, revolutionizing medical approaches. This study aimed to assess the impact of genetic testing on the current epilepsy management paradigm with a specific focus on the variability of outcomes subsequent to genetic diagnoses.

Methodology

Data were collected retrospectively from a cohort of children aged 1-18 years, diagnosed with refractory epilepsy of confirmed genetic origin. The participants received care at a quaternary care center's pediatric neurology clinic from August 2019 to June 2021. The collected information included demographic characteristics, seizure types, EEG findings, imaging abnormalities, genetic diagnoses, attempted treatments, and seizure outcomes.

Results

Among the 210 children with confirmed genetic diagnoses, 74 were included in the study. The gender distribution comprised 45 males and 29 females. Within the cohort, 68/74 exhibited single gene variations, with 23 cases associated with sodium/potassium/calcium channelopathies. Precision medicine could be applied to 25/74 cases. 17/74 children (22.97%) experienced a reduction of up to 50% in seizure frequency due to precision medicine implementation.

Conclusion

While our study indicates the significance of genetic insights in adapting treatment approaches for pediatric epilepsy, it is important to temper our conclusions. The retrospective nature of our study confines our ability to definitively gauge the extent of precision medicine's utility. Our findings suggest the potential of genetic information to enhance epilepsy management, but the true impact of precision medicine can only be established through prospective investigations.

In vitro effects of eslicarbazepine (S-licarbazepine) as a potential precision therapy on SCN8A variants causing neuropsychiatric disorders

BACKGROUND AND PURPOSE

Variants in SCN8A, the Na_V 1.6 channel's coding gene, are characterized by a variety of symptoms, including intractable epileptic seizures, psychomotor delay, progressive cognitive decline, autistic features, ataxia or dystonia. Standard anticonvulsant treatment has a limited impact on the course of disease.

EXPERIMENTAL APPROACH

We investigated the therapeutic potential of eslicarbazepine (S-licarbazepine; S-lic), an enhancer of slow inactivation of voltage gated sodium channels, on two variants with biophysical and neuronal gain-of-function (G1475R and M1760I) and one variant with biophysical gain-of-function but neuronal loss-of-function (A1622D) in neuroblastoma cells and in murine primary hippocampal neuron cultures. These three variants cover the broad spectrum of Na_V 1.6-associated disease and are linked to representative phenotypes of mild to moderate epilepsy (G1475R), developmental and epileptic encephalopathy (M1760I) and intellectual disability without epilepsy (A1622D).

KEY RESULTS

Similar to known effects on Na_V 1.6 wildtype channels, S-lic predominantly enhances slow inactivation on all tested variants, irrespective of their particular biophysical mechanisms. Beyond that, S-lic exhibits variant-specific effects including a partial reversal of pathologically slowed fast inactivation dynamics (A1622D and M1760I) and a trend to reduce enhanced persistent Na⁺ current by A1622D variant channels. Furthermore, our data in primary transfected neurons reveal that not only variant-associated hyperexcitability (M1760I and G1475R) but also hypoexcitability (A1622D) can be modulated by S-lic.

CONCLUSIONS AND IMPLICATIONS

S-lic has not only substance-specific effects but also variant-specific effects. Personalized treatment regimens optimized to achieve such variant-specific pharmacological modulation may help to reduce adverse side effects and improve the overall therapeutic outcome of SCN8A-related disease.

The emergence of genotypic divergence and future precision medicine applications

Genotypic divergence is a term adapted from population genetics and intimately linked to evolution. We use divergence here to emphasize the differences that set individuals apart in any cohort. The history of genetics is filled with descriptions of genotypic differences, but causal inference of interindividual biological variation has been scarce. We suggest that the practice of precision medicine requires a divergent approach, an approach dependent on the causal interpretation of previous convergent (and preliminary) knowledge in the field. This knowledge has relied on convergent descriptive syndromology (lumping), which has overemphasized a reductionistic gene determinism on the quest of seeking associations without causal understanding. Regulatory variants with small effect and somatic mutations are some of the modifying factors that lead to incomplete penetrance and intrafamilial variable expressivity often observed in apparently monogenic clinical disorders. A truly divergent approach to precision medicine requires splitting, that is, the consideration of different layers of genetic phenomena that interact causally in a nonlinear fashion. This chapter reviews convergences and divergences in genetics and genomics, aiming to discuss what can be causally understood to approximate the as-yet utopian lands of Precision Medicine for patients with neurodegenerative disorders.

Gene variant effects across sodium channelopathies predict function and guide precision therapy

Pathogenic variants in the voltage-gated sodium channel gene family lead to early onset epilepsies, neurodevelopmental disorders, skeletal muscle channelopathies, peripheral neuropathies and cardiac arrhythmias. Disease-associated variants have diverse functional effects ranging from complete loss-of-function to marked gain-of-function. Therapeutic strategy is likely to depend on functional effect. Experimental studies offer important insights into channel function but are resource intensive and only performed in a minority of cases. Given the evolutionarily conserved nature of the sodium channel genes, we investigated whether similarities in biophysical properties between different voltage-gated sodium channels can predict function and inform precision treatment across sodium channelopathies. We performed a systematic literature search identifying functionally assessed variants in any of the nine voltage-gated sodium channel genes until 28 April 2021. We included missense variants that had been electrophysiologically characterized in mammalian cells in whole-cell patch-clamp recordings. We performed an alignment of linear protein sequences of all sodium channel genes and correlated variants by their overall functional effect on biophysical properties. Of 951 identified records, 437 sodium channel-variants met our inclusion criteria and were reviewed for functional properties. Of these, 141 variants were epilepsy-associated (SCN1/2/3/8A), 79 had a neuromuscular phenotype (SCN4/9/10/11A), 149 were associated with a cardiac phenotype (SCN5/10A) and 68 (16%) were considered benign. We detected 38 missense variant pairs with an identical disease-associated variant in a different sodium channel gene. Thirty-five out of 38 of those pairs resulted in similar functional consequences, indicating up to 92% biophysical agreement between corresponding sodium channel variants (odds ratio = 11.3; 95% confidence interval = 2.8 to 66.9; P < 0.001). Pathogenic missense variants were clustered in specific functional domains, whereas population variants were significantly more frequent across non-conserved domains (odds ratio = 18.6; 95% confidence interval = 10.9-34.4; P < 0.001). Pore-loop regions were frequently associated with loss-of-function variants, whereas inactivation sites were associated with gain-of-function (odds ratio = 42.1, 95% confidence interval = 14.5-122.4; P < 0.001), whilst variants occurring in voltage-sensing regions comprised a range of gain- and loss-of-function effects. Our findings suggest that biophysical characterisation of variants in one SCN-gene can predict channel function across different SCN-genes where experimental data are not available. The collected data represent the first gain- versus loss-of-function topological map of SCN proteins indicating shared patterns of biophysical effects aiding variant analysis and guiding precision therapy. We integrated our findings into a free online webtool to facilitate functional sodium channel gene variant interpretation (http://SCN-viewer.broadinstitute.org).

Genome sequencing of 320 Chinese children with epilepsy: a clinical and molecular study

The aim of this study is to evaluate the diagnostic value of genome sequencing in children with epilepsy, and to provide genome sequencing-based insights into the molecular genetic mechanisms of epilepsy to help establish accurate diagnoses, design appropriate treatments and assist in genetic counselling. We performed genome sequencing on 320 Chinese children with epilepsy, and interpreted single-nucleotide variants and copy number variants of all samples. The complete pedigree and clinical data of the probands were established and followed up. The clinical phenotypes, treatments, prognoses and genotypes of the patients were analysed. Age at seizure onset ranged from 1 day to 17 years, with a median of 4.3 years. Pathogenic/likely pathogenic variants were found in 117 of the 320 children (36.6%), of whom 93 (29.1%) had single-nucleotide variants, 22 (6.9%) had copy number variants and two had both single-nucleotide variants and copy number variants. Single-nucleotide variants were most frequently found in SCN1A (10/95, 10.5%), which is associated with Dravet syndrome, followed by PRRT2 (8/95, 8.4%), which is associated with benign familial infantile epilepsy, and TSC2 (7/95, 7.4%), which is associated with tuberous sclerosis. Among the copy number variants, there were three with a length <25 kilobases. The most common recurrent copy number variants were 17p13.3 deletions (5/24, 20.8%), 16p11.2 deletions (4/24, 16.7%), and 7q11.23 duplications (2/24, 8.3%), which are associated with epilepsy, developmental retardation and congenital abnormalities. Four particular 16p11.2 deletions and two 15q11.2 deletions were considered to be susceptibility factors contributing to neurodevelopmental disorders associated with epilepsy. The diagnostic yield was 75.0% in patients with seizure onset during the first postnatal month, and gradually decreased in patients with seizure onset at a later age. Forty-two patients (13.1%) were found to be specifically treatable for the underlying genetic cause identified by genome sequencing. Three of them received corresponding targeted therapies and demonstrated favourable prognoses. Genome sequencing provides complete genetic diagnosis, thus enabling individualized treatment and genetic counselling for the parents of the patients. Genome sequencing is expected to become the first choice of methods for genetic testing of patients with epilepsy.

Approach to Neurological Channelopathies and Neurometabolic Disorders in Newborns

Ion channel disorders (channelopathies) can affect any organ system in newborns before 2 months of life, including the skeletal muscle and central nervous system. Channelopathies in newborns can manifest as seizure disorders, which is a critical issue as early onset seizures can mimic the presentation of neurometabolic disorders. Seizures in channelopathies can either be focal or generalized, and range in severity from benign to epileptic encephalopathies that may lead to developmental regression and eventually premature death. The presenting symptoms of channelopathies are challenging for clinicians to decipher, such that an extensive diagnostic survey through a precise step-by-step process is vital. Early diagnosis of a newborn's disease, either as a channelopathy or neurometabolic disorder, is important for the long-term neurodevelopment of the child.

SCN8A-related developmental and epileptic encephalopathy with ictal asystole requiring cardiac pacemaker implantation

INTRODUCTION

SCN8A-related epilepsy has various phenotypes. In particular, patients with developmental and epileptic encephalopathy (DEE) are resistant to antiepileptic drugs and may present with autonomic symptoms, such as marked bradycardia and apnea during seizures, and thus have an increased risk of sudden death. Herein, we report a case of very severe SCN8A-related epilepsy necessitating cardiac pacemaker implantation because of repetitive ictal asystole.

CASE REPORT

The patient was a 14-month-old girl. Tremor and generalized tonic seizure occurred after birth. During seizures, bradycardia and perioral cyanosis occurred, and then, after developing tachycardia and apnea, marked bradycardia and generalized cyanosis occurred, which sometimes resulted in ictal asystole requiring cardiopulmonary resuscitation. Her seizures were refractory to antiepileptic drugs. As the seizures requiring resuscitation did not decrease, cardiac pacemaker implantation was performed four months after birth. Exome sequencing revealed a heterozygous de novo variant in SCN8A (NM_014191.3:c.4934T>C,p.(Met1645Thr)). Even though phenytoin was effective, seizures with bradycardia remained approximately once a month, and pacemaker activity was observed.

CONCLUSIONS

This is, to our knowledge, the first reported case of SCN8A-related DEE in whom pacemaker implantation was performed. Pacemaker implantation should be considered as a treatment option for critical patients with SCN8A-related DEE as in the present case, because the incidence of sudden unexpected death in epilepsy is reported to be approximately 10% in patients with SCN8A-related DEE.

Rational Small Molecule Treatment for Genetic Epilepsies

Genetic testing has yielded major advances in our understanding of the causes of epilepsy. Seizures remain resistant to treatment in a significant proportion of cases, particularly in severe, childhood-onset epilepsy, the patient population in which an underlying causative genetic variant is most likely to be identified. A genetic diagnosis can be explanatory as to etiology, and, in some cases, might suggest a therapeutic approach; yet, a clear path from genetic diagnosis to treatment remains unclear in most cases. Here, we discuss theoretical considerations behind the attempted use of small molecules for the treatment of genetic epilepsies, which is but one among various approaches currently under development. We explore a few salient examples and consider the future of the small molecule approach for genetic epilepsies. We conclude that significant additional work is required to understand how genetic variation leads to dysfunction of epilepsy-associated protein targets, and how this impacts the function of diverse subtypes of neurons embedded within distributed brain circuits to yield epilepsy and epilepsy-associated comorbidities. A syndrome- or even variant-specific approach may be required to achieve progress. Advances in the field will require improved methods for large-scale target validation, compound identification and optimization, and the development of accurate model systems that reflect the core features of human epilepsy syndromes, as well as novel approaches towards clinical trials of such compounds in small rare disease cohorts.

Electrophysiological Biomarkers in Genetic Epilepsies

Precision treatments for epilepsy targeting the underlying genetic diagnoses are becoming a reality. Historically, the goal of epilepsy treatments was to reduce seizure frequency. In the era of precision medicine, however, outcomes such as prevention of epilepsy progression or even improvements in cognitive functions are both aspirational targets for any intervention. Developing methods, both in clinical trial design and in novel endpoints, will be necessary for measuring, not only seizures, but also the other neurodevelopmental outcomes that are predicted to be targeted by precision treatments. Biomarkers that quantitatively measure disease progression or network level changes are needed to allow for unbiased measurements of the effects of any gene-level treatments. Here, we discuss some of the promising electrophysiological biomarkers that may be of use in clinical trials of precision therapies, as well as the difficulties in implementing them.

Predicting functional effects of missense variants in voltage-gated sodium and calcium channels

Malfunctions of voltage-gated sodium and calcium channels (encoded by SCNxA and CACNA1x family genes, respectively) have been associated with severe neurologic, psychiatric, cardiac, and other diseases. Altered channel activity is frequently grouped into gain or loss of ion channel function (GOF or LOF, respectively) that often corresponds not only to clinical disease manifestations but also to differences in drug response. Experimental studies of channel function are therefore important, but laborious and usually focus only on a few variants at a time. On the basis of known gene-disease mechanisms of 19 different diseases, we inferred LOF (n = 518) and GOF (n = 309) likely pathogenic variants from the disease phenotypes of variant carriers. By training a machine learning model on sequence- and structure-based features, we predicted LOF or GOF effects [area under the receiver operating characteristics curve (ROC) = 0.85] of likely pathogenic missense variants. Our LOF versus GOF prediction corresponded to molecular LOF versus GOF effects for 87 functionally tested variants in SCN1/2/8A and CACNA1I (ROC = 0.73) and was validated in exome-wide data from 21,703 cases and 128,957 controls. We showed respective regional clustering of inferred LOF and GOF nucleotide variants across the alignment of the entire gene family, suggesting shared pathomechanisms in the SCNxA/CACNA1x family genes.

Utility of genetic testing for therapeutic decision-making in adults with epilepsy

OBJECTIVE

Genetic testing has become a routine part of the diagnostic workup in children with early onset epilepsies. In the present study, we sought to investigate a cohort of adult patients with epilepsy, to determinate the diagnostic yield and explore the gain of personalized treatment approaches in adult patients.

METHODS

Two hundred patients (age span = 18-80 years) referred for diagnostic gene panel testing at the Danish Epilepsy Center were included. The vast majority (91%) suffered from comorbid intellectual disability. The medical records of genetically diagnosed patients were mined for data on epilepsy syndrome, cognition, treatment changes, and seizure outcome following the genetic diagnosis.

RESULTS

We found a genetic diagnosis in 46 of 200 (23%) patients. SCN1A, KCNT1, and STXBP1 accounted for the greatest number of positive findings (48%). More rare genetic findings included SLC2A1, ATP6A1V, HNRNPU, MEF2C, and IRF2BPL. Gene-specific treatment changes were initiated in 11 of 46 (17%) patients (one with SLC2A1, 10 with SCN1A) following the genetic diagnosis. Ten patients improved, with seizure reduction and/or increased alertness and general well-being.

SIGNIFICANCE

With this study, we show that routine diagnostic testing is highly relevant in adults with epilepsy. The diagnostic yield is similar to previously reported pediatric cohorts, and the genetic findings can be useful for therapeutic decision-making, which may lead to better seizure control, ultimately improving quality of life.

NaV1.1 and NaV1.6 selective compounds reduce the behavior phenotype and epileptiform activity in a novel zebrafish model for Dravet Syndrome

Dravet syndrome is caused by dominant loss-of-function mutations in SCN1A which cause reduced activity of Nav1.1 leading to lack of neuronal inhibition. On the other hand, gain-of-function mutations in SCN8A can lead to a severe epileptic encephalopathy subtype by over activating NaV1.6 channels. These observations suggest that Nav1.1 and Nav1.6 represent two opposing sides of the neuronal balance between inhibition and activation. Here, we hypothesize that Dravet syndrome may be treated by either enhancing Nav1.1 or reducing Nav1.6 activity. To test this hypothesis we generated and characterized a novel DS zebrafish model and tested new compounds that selectively activate or inhibit the human NaV1.1 or NaV1.6 channel respectively. We used CRISPR/Cas9 to generate two separate Scn1Lab knockout lines as an alternative to previous zebrafish models generated by random mutagenesis or morpholino oligomers. Using an optimized locomotor assay, spontaneous burst movements were detected that were unique to Scn1Lab knockouts and disappear when introducing human SCN1A mRNA. Besides the behavioral phenotype, Scn1Lab knockouts show sudden, electrical discharges in the brain that indicate epileptic seizures in zebrafish. Scn1Lab knockouts showed increased sensitivity to the GABA antagonist pentylenetetrazole and a reduction in whole organism GABA levels. Drug screenings further validated a Dravet syndrome phenotype. We tested the NaV1.1 activator AA43279 and two novel NaV1.6 inhibitors MV1369 and MV1312 in the Scn1Lab knockouts. Both type of compounds significantly reduced the number of spontaneous burst movements and seizure activity. Our results show that selective inhibition of NaV1.6 could be just as efficient as selective activation of NaV1.1 and these approaches could prove to be novel potential treatment strategies for Dravet syndrome and other (genetic) epilepsies. Compounds tested in zebrafish however, should always be further validated in other model systems for efficacy in mammals and to screen for potential side effects.

Biological concepts in human sodium channel epilepsies and their relevance in clinical practice

OBJECTIVE

Voltage-gated sodium channels (SCNs) share similar amino acid sequence, structure, and function. Genetic variants in the four human brain-expressed SCN genes SCN1A/2A/3A/8A have been associated with heterogeneous epilepsy phenotypes and neurodevelopmental disorders. To better understand the biology of seizure susceptibility in SCN-related epilepsies, our aim was to determine similarities and differences between sodium channel disorders, allowing us to develop a broader perspective on precision treatment than on an individual gene level alone.

METHODS

We analyzed genotype-phenotype correlations in large SCN-patient cohorts and applied variant constraint analysis to identify severe sodium channel disease. We examined temporal patterns of human SCN expression and correlated functional data from in vitro studies with clinical phenotypes across different sodium channel disorders.

RESULTS

Comparing 865 epilepsy patients (504 SCN1A, 140 SCN2A, 171 SCN8A, four SCN3A, 46 copy number variation [CNV] cases) and analysis of 114 functional studies allowed us to identify common patterns of presentation. All four epilepsy-associated SCN genes demonstrated significant constraint in both protein truncating and missense variation when compared to other SCN genes. We observed that age at seizure onset is related to SCN gene expression over time. Individuals with gain-of-function SCN2A/3A/8A missense variants or CNV duplications share similar characteristics, most frequently present with early onset epilepsy (<3 months), and demonstrate good response to sodium channel blockers (SCBs). Direct comparison of corresponding SCN variants across different SCN subtypes illustrates that the functional effects of variants in corresponding channel locations are similar; however, their clinical manifestation differs, depending on their role in different types of neurons in which they are expressed.

SIGNIFICANCE

Variant function and location within one channel can serve as a surrogate for variant effects across related sodium channels. Taking a broader view on precision treatment suggests that in those patients with a suspected underlying genetic epilepsy presenting with neonatal or early onset seizures (<3 months), SCBs should be considered.

Impact on Clinical Decision Making of Next-Generation Sequencing in Pediatric Epilepsy in a Tertiary Epilepsy Referral Center

Background. Next-generation sequencing (NGS) describes new powerful techniques of nucleic acid analysis, which allow not only disease gene identification diagnostics but also applications for transcriptome/methylation analysis and meta-genomics. NGS helps identify many monogenic epilepsy syndromes. Pediatric epilepsy patients can be tested using NGS epilepsy panels to diagnose them, thereby influencing treatment choices. The primary objective of this study was to evaluate the impact of genetic testing on clinical decision making in pediatric epilepsy patients. Methods. We completed a single-center retrospective cohort study of 91 patients (43 male) aged 19 years or less undergoing NGS with epilepsy panels differing in size ranging from 5 to 434 genes from October 2013 to September 2017. Results. During a mean time of 3.6 years between symptom onset and genetic testing, subjects most frequently showed epileptic encephalopathy (40%), focal epilepsy (33%), and generalized epilepsy (18%). In 16 patients (18% of the study population), "pathogenic" or "likely pathogenic" results according to ACMG criteria were found. Ten of the 16 patients (63%) experienced changes in clinical management regarding their medication and avoidance of further diagnostic evaluation, that is, presurgical evaluation. Conclusion. NGS epilepsy panels contribute to the diagnosis of pediatric epilepsy patients and may change their clinical management with regard to both preventing unnecessary and potentially harmful diagnostic procedures and management. Thus, the present data support the early implementation in order to adopt clinical management in selected cases and prevent further invasive investigations. Given the relatively small sample size and heterogeneous panels a larger prospective study with more homogeneous panels would be helpful to further determine the impact of NGS on clinical decision making.

Recent advances in treatment of epilepsy-related sodium channelopathies

Voltage-gated sodium channels (VGSCs) play a crucial role in generation of action potentials. Pathogenic variants in the five human brain expressed VGSC genes, SCN1A, SCN2A, SCN3A, SCN8A and SCN1B have been associated with a spectrum of epilepsy phenotypes and neurodevelopmental disorders. In the last decade, next generation sequencing techniques have revolutionized the way we diagnose these channelopathies, which is paving the way towards precision medicine. Knowing the functional effect (Loss-of-function versus Gain-of-function) of a variant is not only important for understanding the underlying pathophysiology, but it is particularly crucial to orient therapeutic decisions. Here we provide a review of the literature dealing with treatment options in epilepsy-related sodium channelopathies, including the current and emerging medications.

Diagnostik genetisch bedingter Epilepsien

Je nach Anfallssemiologie und EEG-Befund werden Epilepsien klinisch zumeist in fokale bzw. generalisierte Formen unterteilt. Tritt bei einem Kind infolge einer Epilepsie zusätzlich eine Entwicklungsstörung auf, kann dies oft auf eine epileptische Enzephalopathie zurückgeführt werden. Das Mutationsspektrum genetischer Epilepsien ist ausgesprochen heterogen und kann am besten mithilfe der Hochdurchsatzsequenzierung erfasst werden. Insbesondere bei den Enzephalopathien besteht eine hohe Aufklärungsrate. Mittlerweile gibt es für diverse genetisch bedingte Epilepsieerkrankungen individualisierte Therapien, die auf den jeweiligen molekularen Pathomechanismus abzielen, und die Zahl solcher personalisierter Therapieoptionen steigt stetig.

A de novo SCN8A heterozygous mutation in a child with epileptic encephalopathy: a case report

Background

Epilepsy is a complex disorder caused by various factors, including genetic aberrance. Recent studies have identified an essential role of the sodium channel Nav1.6, encoded by the gene SCN8A, in epileptic encephalopathy.

Case presentation

Using parent-offspring trio targeted-exome sequencing, we identified a de novo heterozygous missense mutation c.3953A > G (p.N1318S) in SCN8A in a 3-year-and-9-month Chinese female patient with early infantile epileptic encephalopathy and a normal magnetic resonance imaging of the brain.

Conclusions

This de novo mutation was only detected in the patient but not in her parents. Bioinformatic analysis indicates the pathogenicity of this mutation. Administration of the sodium channel blocker well controlled seizures in the patient. Therefore, we recommend trio targeted-exome sequencing as a routine method for pathogenic variant screening in patients with intractable epilepsy and a normal MRI.

A single-center SCN8A-related epilepsy cohort: clinical, genetic, and physiologic characterization

Objective

Pathogenic variants in SCN8A, encoding the voltage‐gated sodium (Na+) channel α subunit Nav1.6, is a known cause of epilepsy. Here, we describe clinical and genetic features of all patients with SCN8A epilepsy evaluated at a single‐tertiary care center, with biophysical data on identified Nav1.6 variants and pharmacological response to selected Na+ channel blockers.

Methods

SCN8A variants were identified via an exome‐based panel of epilepsy‐associated genes for next generation sequencing (NGS), or via exome sequencing. Biophysical characterization was performed using voltage‐clamp recordings of ionic currents in heterologous cells.

Results

We observed a range in age of onset and severity of epilepsy and associated developmental delay/intellectual disability. Na+ channel blockers were highly or partially effective in most patients. Nav1.6 variants exhibited one or more biophysical defects largely consistent with gain of channel function. We found that clinical severity was correlated with the presence of multiple observed biophysical defects and the extent to which pathological Na+ channel activity could be normalized pharmacologically. For variants not previously reported, functional studies enhanced the evidence of pathogenicity.

Interpretation

We present a comprehensive single‐center dataset for SCN8A epilepsy that includes clinical, genetic, electrophysiologic, and pharmacologic data. We confirm a spectrum of severity and a variety of biophysical defects of Nav1.6 variants consistent with gain of channel function. Na+ channel blockers in the treatment of SCN8A epilepsy may correlate with the effect of such agents on pathological Na+ current observed in heterologous systems.

Generalized tonic seizures with autonomic signs are the hallmark of SCN8A developmental and epileptic encephalopathy

Developmental and epileptic encephalopathy (DEE) due to SCN8A gene variants is characterized by drug-resistant early onset epilepsy associated with severe intellectual disability. Different seizure types have been reported, and a sequence of autonomic manifestations such as brady-/tachycardia, irregular breathing, and cyanosis. Nevertheless, an exhaustive video-polygraphic documentation is still lacking. In this study, we reviewed the ictal electroencephalograms (EEGs) of five patients with SCN8A-DEE followed-up at the Neuroscience Department at Bambino Gesù Children's Hospital in Rome. We identified generalized tonic seizure as the major seizure type at epilepsy onset. Seizure severity could vary from subtle to marked clinical manifestations, depending from the extent and groups of muscles involved and association with autonomic modifications. We found autonomic signs in 80% of seizures in our cases, and we were able to identify a stereotyped sequence of ictal events for most of seizures. Autonomic signs occurred in rapid sequence: flushing of the face, sometimes associated with sialorrhea, bradycardia, and hypopnea appeared within the first 1-2 s. Tachycardia, polypnea, perioral cyanosis, and pallor occurred later in the course of the seizure. Generalized tonic seizures are rarely described in other genetic epileptic conditions of early infancy because of ion channel mutations, such as in DEE due to KCNQ2 or SCN2A gene mutations, where seizures are most frequently reported as focal to bilateral tonic. Therefore, generalized symmetric tonic seizures with autonomic signs can be considered a clinical hallmark for diagnosis of SCN8A-related DEE and relevant for therapeutic implications.

Clinical study of 19 patients with SCN8A-related epilepsy: Two modes of onset regarding EEG and seizures

OBJECTIVE

To describe the mode of onset of SCN8A-related severe epilepsy in order to facilitate early recognition, and eventually early treatment with sodium channel blockers.

METHODS

We reviewed the phenotype of patients carrying a mutation in the SCN8A gene, among a multicentric cohort of 638 patients prospectively followed by several pediatric neurologists. We focused on the way clinicians made the diagnosis of epileptic encephalopathy, the very first symptoms, electroencephalography (EEG) findings, and seizure types. We made genotypic/phenotypic correlation based on epilepsy-associated missense variant localization over the protein.

RESULTS

We found 19 patients carrying a de novo mutation of SCN8A, representing 3% of our cohort, with 9 mutations being novel. Age at onset of epilepsy was 1 day to 16 months. We found two modes of onset: 12 patients had slowly emerging onset with rare and/or subtle seizures and normal interictal EEG (group 1). The first event was either acute generalized tonic-clonic seizure (GTCS; Group 1a, n = 6) or episodes of myoclonic jerks that were often mistaken for sleep-related movements or other movement disorders (Group 1b, n = 6). Seven patients had a sudden onset of frequent tonic seizures or epileptic spasms with abnormal interictal EEG leading to rapid diagnosis of epileptic encephalopathy. Sodium channel blockers were effective or nonaggravating in most cases.

SIGNIFICANCE

SCN8A is the third most prevalent early onset epileptic encephalopathy gene and is associated with two modes of onset of epilepsy.

SCN8A mutations in Chinese patients with early onset epileptic encephalopathy and benign infantile seizures

Background

SCN8A mutations have recently been associated with epilepsy and neurodevelopmental disorders. This study aimed to broaden the phenotypic-spectrum of disease related with SCN8A mutations.

Methods

To identify the pathogenic gene of a Chinese family, in which six members suffered from epilepsy, whole-exome sequencing was performed. In addition, target next-generation sequencing (NGS) was performed on 178 sporadic patients, who had epilepsy of unknown etiology within 6 months after birth. A detailed clinical history was obtained.

Results

A heterozygous missense mutation of SCN8A was identified in the Chinese family. Six de novo mutations of SCN8A were detected in 6 sporadic patients with epilepsy. In the family, six members developed seizures within a few years after birth. Five of them had milder clinical performance, that they had normal cognition and developmental milestones, and seizure-free was achieved by mono-therapy. The other one affected member presented with refractory epilepsy and developmental regression. She died from sudden unexpected death in epilepsy (SUDEP) at 17-year-old. Clinical features of six sporadic patients with SCN8A mutations were diverse, ranging from severe epileptic encephalopathy to benign epilepsy with normal cognition. Seizures started at the mean age of 3.9 months (from 2 months to 6 months). Seizure-free was achieved in four of them by mono- or multi-antiepileptic drugs. Five of them demonstrated mild or severe psychomotor retardation, whereas the other one was normal in development and intelligence.

Conclusions

Our findings extend the spectrum of SCN8A mutations and the clinical features of patients with SCN8A mutations. The majority of SCN8A mutations were de novo, inherited mutations from the heterozygous parents can also occur. The phenotypic spectrum of SCN8A mutation varied largely. Most affected patients manifested as refractory epilepsy and severe intellectual disability, only a small number of patients presented with milder clinical patterns. Additionally, our study confirmed that the same mutation can lead to different phenotypes.

Electronic supplementary material

The online version of this article (10.1186/s12881-017-0460-1) contains supplementary material, which is available to authorized users.

Autosomal dominant SCN8A mutation with an unusually mild phenotype

BACKGROUND

Mutations in SCN8A, coding for the voltage-gated sodium channel Nav 1.6, have been described in relation to infantile onset epilepsy with developmental delay and cognitive impairment, in particular early onset epileptic encephalopathy (EIEE) type 13.

CASE REPORT

Here we report an infant and his father with early onset focal epileptic seizures but without cognitive or neurological impairment in whom next generation sequence analysis identified a heterozygous mutation (c.5630A > G, p. (Asn1877Ser)) in the SCN8A gene. This mutation, confirmed by Sanger sequence analysis, affects a highly conserved amino acid and in silico tools predicts that it may be pathogenic. The reported infant has a normal developmental profile at 16-month follow-up. His father also had normal development and has no cognitive impairment at 42 years. This is the second known SCN8A mutation associated with a phenotype of benign familial infantile epilepsy. Good seizure control was achieved in our patients with sodium channel blockers.

CONCLUSION

Based on our proband and a recently described group of families with benign familial infantile epilepsy and SCN8A variant we suggest expanding testing to patients with infantile epilepsy and no cognitive impairment. In addition, the same SCN8A variant (c.5630A > G, p. (Asn1877Ser)) is also found in patients with epilepsy and developmental delay highlighting the phenotypic variability and the possible role of other protective genetic factors.

Gene Panel Testing in Epileptic Encephalopathies and Familial Epilepsies

In recent years, several genes have been causally associated with epilepsy. However, making a genetic diagnosis in a patient can still be difficult, since extensive phenotypic and genetic heterogeneity has been observed in many monogenic epilepsies. This study aimed to analyze the genetic basis of a wide spectrum of epilepsies with age of onset spanning from the neonatal period to adulthood. A gene panel targeting 46 epilepsy genes was used on a cohort of 216 patients consecutively referred for panel testing. The patients had a range of different epilepsies from benign neonatal seizures to epileptic encephalopathies (EEs). Potentially causative variants were evaluated by literature and database searches, submitted to bioinformatic prediction algorithms, and validated by Sanger sequencing. If possible, parents were included for segregation analysis. We identified a presumed disease-causing variant in 49 (23%) of the 216 patients. The variants were found in 19 different genes including SCN1A, STXBP1, CDKL5, SCN2A, SCN8A, GABRA1, KCNA2, and STX1B. Patients with neonatal-onset epilepsies had the highest rate of positive findings (57%). The overall yield for patients with EEs was 32%, compared to 17% among patients with generalized epilepsies and 16% in patients with focal or multifocal epilepsies. By the use of a gene panel consisting of 46 epilepsy genes, we were able to find a disease-causing genetic variation in 23% of the analyzed patients. The highest yield was found among patients with neonatal-onset epilepsies and EEs.